1. Field of the Invention
The present invention relates to an inkjet recording apparatus for performing image evaluation of an image which is formed on a recording medium by an inkjet method using a liquid functional material (ink).
2. Background Art
The engineering/industrial printing utilizing an inkjet system is advantageous to small-lot printing and its development is being increasingly promoted in recent years. Particularly, an active energy curing-type inkjet recording apparatus in which a liquid functional material (ink) capable of being cured by active energy such as electron beam and ultraviolet ray is fed, ejected on a recording medium by using an inkjet head and cured under energy irradiation, thereby performing image formation, is assured of characteristic features, in terms of the property of the ink itself, which can satisfy various requirements such as high-speed recording on a recording medium, less blurring and high-definition image, and environment-friendliness. Above all, as for the apparatus using an ink curable by an ultraviolet ray which is the active energy, several systems have been proposed in view of easy handling of the light source, compact fabrication and the like. Furthermore, when a full-line type inkjet head having a plurality of heads arranged to cover the entire width of the recording medium and an ultraviolet-curable ink requiring no drying step in many cases are combined, higher-speed recording can be achieved.
The inkjet recording apparatus using a full-line type inkjet head has many ejection nozzles and therefore, when ejection failure of the ejection nozzle occurs, this is visible as an image defect. In an inkjet recording apparatus required to process a large amount of image, a roll paper-feeding system of forming an image on a continuous recording medium is generally employed. In the roll paper-feeding system, the recording medium continues from before image drawing until take-up through processing and an arbitrary image of, for example, a recording medium having formed thereon a pattern for image evaluation is difficult to directly take out immediately after the image formation and confirm with an eye.
On the other hand, in order to keep constant the image quality, it is necessary to periodically or aperiodically perform image evaluation, for example, at the exchange of inkjet head or after image formation on a large number of sheets, and feed back the evaluation results. Conventionally, the image evaluation of an image formed by a full-line type inkjet recording apparatus using such a continuous recording medium has been effected by stopping the image formation and observing the image on the recording medium or performing on-line scanning (see, for example, JP-A-2001-277673 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
However, in the image evaluation on the recording medium, the image formation must be stopped, or a plurality of evaluation images cannot be compared and evaluated or can be hardly compared under a correct light source, making it difficult to perform image evaluation sufficient to keep constant the image quality.
In the inkjet recording apparatus disclosed in JP-A-2001-277673, a test pattern is printed in the state of a roll paper (continuous recording medium) being held between a pair of paper conveying/holding roller and paper discharging roller, and the image formed on the roll paper is read in an imaging part comprising an image pickup device such as CCD (on-line scanning) while again conveying the roll paper after once unrolling it or while conveying the roll paper in the direction opposite to that at the printing, whereby image evaluation is performed. However, there is a problem that reading of the image takes much time, making it mandatory to decrease the operation efficiency or sacrifice the evaluation accuracy by reducing the image resolution, and the image formed on the roll paper cannot be evaluated efficiently and properly.